A 70 kg mass is on the edge of a cliff and falls 40 meters before striking a surface where it stops. What is its potential energy? How much kinetic energy does the mass have just before it strikes the surface? What is the velocity of the mass just before it strikes the surface? How much momentum does the mass have just before it strikes the surface?

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".